Fluid availability, fatigue, and inhibition: neuromuscular responses of non-exercised skeletal muscle to load carriage in the heat.

PURPOSE: To investigate the effects of water availability on neuromuscular performance of non-exercising muscles during loaded marching in the heat. METHODS: Ten physically active adults (7 men, 3 women; age 27.4 ± 6.8 y; body mass 76.6 ± 9.3 kg; V̇O2peak 58.6 ± 12.7 ml·kg⁻¹·min⁻¹) completed 2 × 60 min discontinuous loaded marches (3 × 20 min) in ~ 30 °C, ~ 60% RH while carrying ~ 10% body mass. Mean marching intensity was ~ 68% HRmax. In one trial, consumed water was ad libitum (DRINK); in the other, water was withheld (NO DRINK). Hydration, heart rate (HR), and thermoregulatory responses (heart rate, core and mean skin temperature) were monitored. Neuromuscular performance of non-exercising muscles (handgrip strength, bite force), thermal sensation (TS), and rating of perceived exertion (RPE) were assessed pre, during, and post march. RESULTS: Percentage body-mass loss was 0.9% (DRINK) vs. 1.6% (NO DRINK; p > 0.05). Sweat rate was higher in DRINK (1.61 ± 0.36 vs. 1.22 ± 0.21 l·h⁻¹; p = 0.006). HR and core temperature rose with workload but did not differ between conditions. TS and RPE were higher in NO DRINK with elevated blood lactate (p < 0.05). Handgrip declined across trials (~ 7%, non-significant), and bite force was unchanged (p > 0.38). CONCLUSION: Withholding water during a 1 h loaded march in heat, TS and RPE but did not impair cardiovascular, thermoregulatory, or the neuromuscular performance of non-exercising muscles. Under these conditions, water restriction did not compromise non-exercising muscle function despite greater perceived effort.